For the manufacture of small-format concrete ware in industrial production the devices now mostly used employ the principle of shock vibration for the compacting of the concrete conglomerate. Systems for the generating of vibration are used with such devices that are based on unbalance shafts driven by electric motors as described in detail, for example, in the article “Increasing the Quality of Production by Efficient Compacting” by Berthold Schlecht and Alexander Neubauer appearing in the periodical “Betonwert+Fertigteil−Technik” at pages 44 to 52 of Issue No. 9/2000. On the underside of the table upon which the input form places the concrete conglomerate, but not tightly mounted, there are attached, respectively, two unbalance shafts or two pairs of unbalance shafts so that, in the latter case, the unbalance shafts are put into forced synchronization either mechanically using gears or electronically. As a rule the input form is thus comprised of a so-called pallet—a plank, a plastic slab, or a steel sheet—and a molding box whose side walls define the concrete ware and lie on the pallet. This is primarily due to reasons of production technology, as the removal of the finished concrete ware is done on these pallets, but the process has also been influenced significantly by shock vibration.
Such devices are burdened by disadvantages, however, in that, for the optimal compacting of the concrete as a rule high momentary accelerations are required of as great as 200 m/s2. With the known devices, however, only unbalance forces of a maximum of 200 kN can be provided because, among other things, the bearings of the rotating unbalances would otherwise be exposed to unacceptably high loads along with very short bearing lifetimes. Given the fact that the high accelerations required cannot be provided by means of the harmonic vibration of the table generated by unbalance agitation, they must be produced by another means. This is done with the assistance of so-called shock vibration. In this manner, the high accelerations necessary are generated, briefly each time, by means of so-called concussion hits between the components of the table, pallet, and mold box that are not tightly connected to each other. Furthermore, the generating of the concussion hits occurs by means of knock ridges arranged in a stationary position parallel to the table. The installation of these knock ridges is done purely empirically by matching various mechanical parameters and thus does not always provide optimum adjustment and optimal compacting. The use of a different concrete or a different form thus entails extensive installation work. Further disadvantages of shock vibration are the high emission of noise connected with the concussion hits, the high mechanical load, and high wear on the equipment. The latter also leads to losing the optimal adjustment of the machine and a worsening of the quality of the product.
If one desires to avoid shock vibration one must make up for the absence of the acceleration peaks generated by concussion hits with the concomitant higher forces in harmonic vibration. However, with the known motorized unbalance agitators such higher forces cannot be created. Indeed, use has been made of one or more hydraulically operated servo cylinders instead of motor-driven unbalance agitators so as to be able to generate the higher forces and to make use of the principle of harmonic vibration. There is also a description of the devices based on hydraulic operation for concrete masonry production in the article by Schlecht and Neubauer mentioned above as well as in Application WO 01/47698 A1. The advantages of harmonic vibration are, among other things, that the wear is significantly reduced, there is a reduction in the noise emissions, as the pallet, mold box, and table are tightly connected in this case, the cement usage can be reduced, and the production times may be significantly reduced.
There is also a disadvantage present in the choice of hydraulics as of the operating method, however. First of all, servo hydraulics require that the oil be extremely clean, which can only be achieved in the environment of a concrete plant with high expenditure. Furthermore, the energy requirements of a device based on hydraulics are distinctly higher than those of the conventional shock vibration devices operated by electric motors. Moreover, the production costs of such a servo hydraulic system are distinctly higher than those for a electric motor drive.
In Application WO 01/47698 A1 it is indeed proposed that harmonic vibrations be generated, but no method is referred to for overcoming the known disadvantages of the state of the art as mentioned above.